Acoustic Levitation – The Science Of Flying With Sound

Levitating objects with Acoustic Levitation (in a standing wave transducer setup)
Levitating objects in a standing wave transducer setup

Don’t you love it when physics makes things fly in mid air using super-cool concepts? Yes, me too! Here’s another example of a stupefying act made possible by Acoustic Levitation.

What is Acoustic Levitation?

A technique which allows matter to float (levitate) in a gas (supposedly air) using the acoustic radiation pressure created by sound waves.

Our elementary understanding of a sound wave tells us that it is made up of compressions and rarefactions in a longitudinally “moving” waveform.

Via Giphy

Compressions are areas with tightly vibrating particles. Rarefactions are areas with loosely vibrating particles inside a medium (gas or air).

How does it work?

Conceptually, when at the apt distance and at the apt frequency, two sound waves traveling toward each other collide, they merge together to form a single sound wave called a Standing Wave.

Via Giphy

Just like a regular sound wave, a standing wave has its own compressions and rarefactions called nodes and antinodes. They form at fixed spots throughout the wave. These tiny pressure spots can withhold little pieces of matter in them which appear to levitate in the air at fixed distances giving rise to acoustic levitation.

The heaviest object ever levitated using the technique, at a frequency of 25KHz, weighs 1.46 grams.

Via Giphy

The method has intriguing applications such as forming perfect spheres of molten materials, and, carrying out uncontaminated chemical reactions which are hard to achieve otherwise.

To us, this concept defies gravity! Who knows the future of hovering vehicles may originate from acoustic levitation! “Sounds” fun, right?